1. Technical Field
The present disclosure relates to systems and methods for controlling an internal combustion engine having at least one spark plug per cylinder with individual plug control and ionization current sensing.
2. Background Art
Manufacturers continue to improve control of internal combustion engines to enhance fuel economy and performance while reducing emissions using more sophisticated sensing and processing hardware and software. To improve control of the combustion process, ionization current sensing (or ion sense) uses a bias voltage applied across a sensor positioned within the combustion chamber to generate a current signal indicative of the combustion quality and timing. For spark-ignition engines, one or more spark plugs may be used as an ion sensor with the bias voltage applied across the air gap of the spark plug, or between a spark plug electrode and the cylinder wall.
One strategy to reduce emissions and improve fuel economy in spark-ignited gasoline fuel-injected internal combustion engines is to increase the combustion burn rate. The faster combustion is helpful to avoid knock and to tolerate larger amounts of exhaust gas recirculation (EGR), which lowers combustion temperatures and generation of oxides of nitrogen (NOx). Additionally, fast burn is desirable for better combustion stability, effectively reducing noise, vibration, and harshness (NVH). For certain combustion chambers, multiple spark plugs may be employed to facilitate fast burn. However, uncontrolled burn rates can result in harsh combustion, which may lead to consumer dissatisfaction. Combustion stability, even with multiple spark plugs, is often difficult to achieve in fast-burn applications. As such, it is desirable to control the combustion process to provide fast-burn combustion stability while avoiding combustion conditions that may be objectionable to vehicle occupants.